In U.S. Pat. Nos. 5,844,086 and 6,005,076 (“Murray II”), assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there is described a process for the isolation of protein isolates from oil seed meal having a significant fat content, including canola oil seed meal having such content. The steps involved in this process include solubilizing proteinaceous material from oil seed meal, which also solubilizes fat in the meal and removing fat from the resulting aqueous protein solution. The aqueous protein solution may be separated from the residual oil seed meal before or after the fat removal step. The defatted protein solution then is concentrated to increase the protein concentration while maintaining the ionic strength substantially constant, after which the concentrated protein solution may be subjected to a further fat removal step. The concentrated protein solution then is diluted to cause the formation of a cloud-like mass of highly aggregated protein molecules as discrete protein droplets in micellar form. The protein micelles are allowed to settle to form an aggregated, coalesced, dense, amorphous, sticky gluten-like protein isolate mass, termed “protein micellar mass” or PMM, which is separated from the residual aqueous phase and dried.
The protein isolate has a protein content (as determined by Kjeldahl Nx 6.25) of at least about 90 wt %, is substantially undenatured (as determined by differential scanning calorimetry) and has a low residual fat content. The term “protein content” as used herein refers to the quantity of protein in the protein isolate expressed on a dry weight basis. The yield of protein isolate obtained using this procedure, in terms of the proportion of protein extracted from the oil seed meal which is recovered as dried protein isolate was generally less than 40 wt %, typically around 20 wt %.
The procedure described in the aforementioned patents was developed as a modification to and improvement on the procedure for forming a protein isolate from a variety of protein source materials, including oil seeds, as described in U.S. Pat. No. 4,208,323 (Murray IB), the disclosure of which is incorporated herein by reference. The oil seed meals available in 1980, when U.S. Pat. No. 4,208,323 issued, did not have the fat contamination levels of canola oil seed meals at the time of Murray II patents, and, as a consequence, the procedure of U.S. Pat. No. 4,208,323 cannot produce from such oil seed meals processed according to the Murray II process, proteinaceous materials which have more than 90 wt % protein content. There is no description of any specific experiments in U.S. Pat. No. 4,208,323 carried out using rapeseed (canola) meal as the starting material.
U.S. Pat. No. 4,208,323 itself was designed to be an improvement on the process described in U.S. Pat. Nos. 4,169,090 and 4,285,862 (Murray IA), incorporated herein by reference, by the introduction of the concentration step prior to dilution to form the PMM. The latter step served to improve the yield of protein isolate from around 20% for the Murray IA process.
In copending U.S. Patent Applications Ser. Nos. 60/288,415 filed May 4, 2001, 60/326,987 filed Oct. 5, 2001, 60/331,066 filed Nov. 7, 2001, 60/333,494 filed Nov. 26, 2001, 60/374,801 filed Apr. 24, 2002, and 10/137,391 filed May 3, 2002, assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there are described further improvements on these prior art protein isolation procedures as they apply to oil seeds to obtain improved yields of dried isolated product protein in terms of the proportion of the protein extracted from the oil seeds which is recovered as protein isolate and to obtain protein isolate of high purity of least about 100 wt % when determined by the Kjeldahl method as percent nitrogen (N) and multiplied by a conversion factor of 6.25 (N×6.25). The procedure is employed particularly to produce a canola protein isolate.
In the procedure described in the aforementioned U.S. Patent Applications Ser. Nos. 60/288,415, 60/326,987, 60/331,066, 60/333,494, 60/372,165, 60/374,801 and Ser. No. 10/137,391, the oil seed meal is extracted with an aqueous food grade salt solution. The resulting protein extract solution, after an initial treatment with a pigment adsorbing agent, if desired, is reduced in volume using ultrafiltration membranes to provide a concentrated protein solution having a protein content of at least about 200 g/L. The concentrated protein solution then is diluted into cold water, resulting in the formation of a white cloud of protein micelles which are allowed to separate. Following removal of the supernatant, the precipitated, viscous sticky mass (PMM) is dried.
In one embodiment of the process described in the aforementioned U.S. Patent Application Ser. No. 60/288,415, as particularly described in copending U.S. Patent Applications Ser. Nos. 60/326,987, 60/331,066, 60/333,494, 60/372,165, 60/374,801 protein isolate comprising dried protein from the wet PMM and from the supernatant. This may be effected by initially concentrating the supernatant using ultrafiltration membranes, generally to a concentration in excess of 100 g/L, mixing the concentrated supernatant with the wet PMM and drying the mixture. The resulting canola protein isolate has a high purity of at least 90 wt %, preferably at least about 100 wt %, (N×6.25).
In another embodiment of the process described in the aforementioned U.S. Patent Application Ser. No. 60/288,415, as particularly described in copending applications Ser. Nos. 60/331,066, 60/333,494, 60/372,165, 60/374,801 and 10/137,391, the supernatant from the PMM settling step is processed to recover a protein isolate therefrom. This procedure may be effected by initially concentrating the supernatant using ultrafiltration membranes generally to a protein concentration of at least about 100 g/L, and drying the concentrated supernatant. The resulting canola protein isolate has a high purity of at least about 90 wt %, preferably at least about 100 wt %, (N×6.25).
In copending U.S. Patent Applications Ser. Nos. 60/331,646 filed Nov. 20, 2001 and 60/383,809 filed May 30, 2002, assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there is described a continuous process for forming oil seed protein isolates from oil seed meal following the procedures of the aforementioned applications but in a continuous manner. By the utilization of a continuous process for the recovery of canola protein isolate as compared to the batch process, the initial protein extraction step can be significantly reduced in time for the same level of protein extraction and significantly higher temperatures can be employed in the extraction step. In addition, in a continuous operation, there is less chance of microbial contamination than in a batch procedure, leading to higher product quality and the process can be carried out in more compact equipment.
In the production of oil seed meal, the oil seed is crushed to remove most of the oil and is hot solvent extracted, generally using hexane, to recover the remainder of the oil. In order to recover the solvent for reuse before the oil seed meal is disposed of by the crusher, the oil seed meal often is heated to a high temperature of about 120° C. to about 140° C. in a procedure termed “toasting”, which drives off residual solvent.
The residual oil seed meal disposed of by the crusher contains significant quantities of protein and often is employed as animal feed. There have been prior attempts to recover the canola protein isolate from the residual canola oil seed meal in the form of a canola protein isolate, following the procedures of the aforementioned Murray patents and of the aforementioned pending patent applications.